Carbon isotopes of trees from arid environments and implications for reconstructing atmospheric CO_2 concentration

Abstract

Four trees from San Dimas, the Santa Monica Mountains and the White Mountains of California, and Sinai Peninsula are studied for carbon isotope ratios. These trees grew in arid environments where vegetation is sparse and canopy effect is minimized. The δ^(13)C time series obtained from wood segments of these trees contain high-frequency variations and a long-term decreasing trend. The high-frequency signals can be effectively explained by the variations of precipitation. The low-frequency trend cannot be accounted for only by the δ^(13)C variation of atmospheric CO_2. The CO_2 concentration in the atmosphere also attributed to the progressive depletion in the ^(13)C contents of these trees. These results indicate a possibility of using δ^(13)C of plants as a proxy indicator of the concentration of atmospheric CO_2, provided that the δ^(13)C value of the open atmosphere can be constrained independently. Plant water-use efficiency is not a simple function of the CO_2 concentration of the atmosphere. It can increase, remain constant, or decrease with an increase of the atmospheric CO_2 concentration.

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